1. Technical Field
The present invention relates to a Rankine cycle configured with a turbine and the organic refrigerants or heat exchange fluids used within the Rankine cycle to drive the turbine. More particularly, the present invention relates to a Rankine cycle and improved organic refrigerants which are particularly useful in driving an electric power generating system and which are highly suited to a wide range of heat sources for providing vapor regeneration of the refrigerants. The heat source may, for example, be exhaust combustion products of a fuel-fired device, hot liquid from a solar collector, geothermal wells, warm ocean waters or a number of other heat sources which typically represent heat sources the heat from which is not captured to provide useful energy or work.
2. Background Information
There is a need to provide electric power which is economical and reliable. There is also a need to provide electric power from sources of energy which are not dependent themselves on electric power to run component parts thereof but can also operate on electric grid in case of a failure of their own electrical power operating system. There is also the need to provide electric power during periods of transmission line power failures in order to maintain electrically-dependent equipment operative. There is also a need to recover energy loss through exhaust combustion products of fuel-fired boilers, for example, and to convert to reusable energy.
There is an urgent need for renewable energy. The renewable energy industry has experienced dramatic changes over the past few years. Deregulation of the electricity market failed to solve the industry's problems. Also, unanticipated increases in localized electricity demands and slower than expected growth in generating capacity have resulted in an urgent need for alternative energy sources, particularly those that are environmentally sound.
Consequently, the renewable energy industry is now in a far different situation than it was when headed into deregulation. Instead of struggling to compete in a competitive deregulated electricity market, renewable energy operators suddenly faced requests to accelerate deployment of new renewable energy capacities and restore facilities that had been closed due to poor economics.
Review of a renewable portfolio may provide some assurance to long term funding of renewable energy facilities and lead to a resurgence in new renewable energy facilities. However, a number of factors and issues will require development of these renewable energy facilities both in the short and long-term.
In the short term, there will be increasing pressure to deploy renewable energy facilities to help add generating capacity, improve system reliability, and stabilize electricity prices. However, the strategic installation of these renewable energy facilities will be hindered by a lack of understanding of how the renewable energy facilities integrate into the existing fossil-based generation systems.
In the long term, these renewable electricity generation systems will require development to benefit the current electricity system. These new systems will require an improved services capacity, be more efficient, relatively cheap to run and maintain and utilize ecologically-friendly chemicals. Developing such systems will largely be tied to growth in the renewable energy distributed generation systems, and will require an understanding and demonstration of renewable energy distributed generation systems which are used in combination with fossil-based generation.
Recent problems in electricity production emphasize the urgent need for a renewable approach to support the current electricity system, increase its existing capacity, and, equally important, benefit the environment by reducing the need to build more power plants and utilize environmentally-friendly chemicals.
One advantage of using organic compounds is that they do not need to be superheated. Unlike steam, organic compounds do not form liquid droplets upon expansion in the turbine. An absence of steam prevents erosion of the turbine blades and enables design flexibility on the heat exchangers.
An Organic Rankine Cycle (ORC) engine is a standard steam engine that utilizes heated vapor to drive a turbine. FIG. 1 illustrates the basic components of an Organic Rankine Cycle. However, this vapor is a heated organic chemical instead of a superheated water steam. The organic chemicals typically used by an ORC include Freon and most of the other traditional refrigerants, such as iso-pentane, chlorofluorocarbons (CFCs), hydrofluorocarbons (HFCs), butane, propane, and ammonia. The traditional refrigerants require high temperature heat sources between 100° C. (212° F.) and 143° C. (290° F.) and cannot operate at temperatures higher than 143° C. and less than 37° C. (100° F.). A refrigerant capable of operating outside these temperature ranges would thus be desirable.